Power generation system

ABSTRACT

This power generation system is provided with: a gas turbine having a compressor, a combustor and a turbine; a first compressed air supply line that supplies compressed air, which has been compressed by the compressor, to the combustor; a solid oxide fuel cell (SOFC) having an air electrode and a fuel electrode; a compressed air supply device capable of generating compressed air; and a second compressed air supply line that supplies compressed air, which has been compressed by the compressed air supply device to the SOFC. The fuel cell can thus be stably operated regardless of the operating state of the gas turbine.

TECHNICAL FIELD

The present invention relates to a power generation system combining afuel cell, a gas turbine, and a steam turbine.

BACKGROUND ART

The solid oxide fuel cell (hereinafter, referred to as SOFC) is known asa high efficiency fuel cell with a wide range of uses. The operatingtemperature of the SOFC is increased to increase the ionic conductivity,so air discharged from the compressor of a gas turbine can be used asair (oxidizing agent) supplied to the air electrode side. Also,high-temperature fuel that could not be used in an SOFC can be used asthe fuel in the combustor of a gas turbine.

Therefore, various combinations of SOFC, gas turbine, and steam turbinehave been proposed as power generation systems that can achieve highefficiency power generation, as disclosed in, for example, PatentDocument 1. The combined system disclosed in Patent Document 1 includesan SOFC, a gas turbine combustor that burns exhaust fuel gas and exhaustair discharged from the SOFC, and a gas turbine having a compressor thatcompresses air for supply to the SOFC.

CITATION LIST Patent Document

Patent Document 1: Japanese Unexamined Patent Application PublicationNo. 2009-205930A

SUMMARY OF THE INVENTION Technical Problem

During normal operation of the conventional power generation systemdescribed above, air compressed by the compressor of the gas turbine issupplied to the combustor of the gas turbine, a portion of the air beingsupplied to the SOFC for use as an oxidizing agent. In this case, thepressure of the air compressed by the compressor fluctuates according tothe operating state of the gas turbine, with the result that thepressure of the compressed air supplied to the SOFC also fluctuatesaccording to the operating state of the gas turbine, leading to the riskof being incapable of maintaining a stable operating state of the SOFC.For example, the power generator is activated through the driving of thegas turbine; if the frequency of the power generator fluctuates, the gasturbine engages in output control in order to keep the frequency at apredetermined frequency. Specifically, the output of the gas turbine isadjusted by adjusting the amount of fuel supplied thereto; during thisprocess, the pressure of the compressed air at the outlet of thecompressor fluctuates, causing the pressure of the compressed airsupplied to the SOFC to also fluctuate.

The present invention solves the problems described above, and has anobject of providing a power generation system allowing a fuel cell to bestably operated regardless of the operating state of a gas turbine.

Solution to Problem

In order to achieve the object proposed above, a power generation systemof the present invention comprises: a gas turbine having a compressorand a combustor; a first compressed air supply line for supplying firstcompressed air compressed by the compressor to the combustor; a fuelcell having an air electrode and a fuel electrode; a compressed airsupply unit capable of generating second compressed air; and a secondcompressed air supply line for supplying second compressed aircompressed by the compressed air supply unit to the fuel cell.

Thus, a compressed air supply unit is provided separately from the gasturbine compressor, with first compressed air compressed by the gasturbine compressor being supplied to the combustor via the firstcompressed air supply line, and second compressed air compressed by thecompressed air supply unit being supplied to the fuel cell via thesecond compressed air supply line. Therefore, there is no fluctuation inthe pressure of the air supplied to the fuel cell even if the pressureof the air supplied to the combustor fluctuates according to theoperating state of the gas turbine. As a result, the fuel cell can bestably operated regardless of the operating state of the gas turbine.

The power generation system of the present invention comprises: a heatrecovery steam generator for generating steam using exhaust gas from thegas turbine; and a steam turbine driven by steam generated by the heatrecovery steam generator, the compressed air supply unit having asteam-driven fuel cell compressor and a steam supply line for supplyingsteam generated by the heat recovery steam generator to the fuel cellcompressor.

Accordingly, when steam generated by the heat recovery steam generatoris supplied to the fuel cell compressor via the steam supply line, thefuel cell compressor is driven by the steam to generate secondcompressed air, which is supplied to the fuel cell. The power generationsystem combines a fuel cell, a gas turbine, and a steam turbine, withsteam generated within the system being used to drive the fuel cellcompressor to generate second compressed air, and the second compressedair being supplied to the fuel cell to improve overall systemefficiency.

In the power generation system of the present invention, the compressedair supply unit includes a fuel cell compressor and a drive motor fordriving the fuel cell compressor.

Accordingly, the fuel cell compressor is driven by the drive motor togenerate second compressed air, which is supplied to the fuel cell.Simply by providing the drive motor and the fuel cell compressor, thesecond compressed air can be supplied to the fuel cell independently ofthe gas turbine, allowing stable operation of the fuel cell to beensured with a simple arrangement.

The power generation system of the present invention comprises: a firston/off valve capable of opening and closing the second compressed airsupply line; a bypass line connecting the first compressed air supplyline and the second compressed air supply line; and a second on/offvalve for opening and closing the bypass line.

Accordingly, the second compressed air generated by driving the fuelcell compressor can be supplied to the combustor via the bypass line,allowing the amount of compressed air to be adjusted according to theoperating state of the gas turbine or the fuel cell.

The power generation system of the present invention comprises a controlunit capable of opening and closing the first on/off valve and thesecond on/off valve, the control unit closing the first on/off valve andopening the second on/off valve when the fuel cell is stopped.

Accordingly, when the fuel cell is stopped, the first on/off valve isclosed to stop the supply of second compressed air from the compressedair supply unit to the fuel cell, and the second on/off valve is openedto start the supply of second compressed air from the compressed airsupply unit to the gas turbine combustor, ensuring the amount ofcompressed air in the gas turbine and allowing the gas turbine tooperate stably.

Effect of the Invention

In accordance with the power generation system of the present invention,first compressed air compressed by the compressor can be supplied to thecombustor and second compressed air compressed by the compressed airsupply unit can be supplied to the fuel cell, allowing the fuel cell tooperate stably regardless of the operating state of the gas turbine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view illustrating a compressed air supply line ina power generation system according to a first embodiment of the presentinvention.

FIG. 2 is a schematic view illustrating the power generation systemaccording to the first embodiment.

FIG. 3 is a schematic view illustrating a compressed air supply line ina power generation system according to a second embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

Preferred embodiments of the power generation system according to thepresent invention will now be described in detail with reference to theattached drawings. The present invention is not limited by theseembodiments, and, when there is a plurality of embodiments,configurations that combine these embodiments are also included.

First Embodiment

The power generation system according to a first embodiment is a TripleCombined Cycle (registered trademark) that combines a solid oxide fuelcell (hereinafter, referred to as SOFC), a gas turbine, and a steamturbine. The Triple Combined Cycle can generate electricity in the threestages of the SOFC, the gas turbine, and the steam turbine by installingthe SOFC on the upstream side of a gas turbine combined cycle powergeneration system (GTCC), so it is possible to achieve extremely highpower generation efficiency.

FIG. 1 is a schematic view illustrating a compressed air supply line inthe power generation system according to the first embodiment of thepresent invention, and FIG. 2 is a schematic view of the configurationof the power generation system according to the first embodiment.

As illustrated in FIG. 2, in the first embodiment, a power generationsystem 10 comprises a gas turbine 11, a generator 12, an SOFC 13, asteam turbine 14, and a generator 15. The power generation system 10 isconfigured to achieve high power generation efficiency by combining thepower generation by the gas turbine 11, the power generation by the SOFC13, and the power generation by the steam turbine 14.

The gas turbine 11 includes a compressor 21, a combustor 22, and aturbine 23, and the compressor 21 and the turbine 23 are connected by arotary shaft 24 so that they rotate integrally. The compressor 21compresses air A that is drawn in from an air intake line 25. Thecombustor 22 mixes and burns compressed air (first compressed air) A1supplied from the compressor 21 via a first compressed air supply line26 and fuel gas L1 supplied via a first fuel gas supply line 27. Theturbine 23 is rotated by exhaust gas (combustion gas) G supplied fromthe combustor 22 via an exhaust gas supply line 28. Although notillustrated on the drawings, the compressed air A1 compressed by thecompressor 21 is supplied to the casing of the turbine 23, and thecompressed air A1 cools the blades and the like as cooling air. Thegenerator 12 is provided coaxially with the turbine 23, and can generatepower by the rotation of the turbine 23. Note that here, for example,liquefied natural gas (LNG) is used as the fuel gas L1 supplied to thecombustor 22.

The SOFC 13 is supplied with high-temperature fuel gas as a reductantand high-temperature air (oxygen gas) as an oxidant, which react at apredetermined operating temperature to generate power. The SOFC 13 isconfigured from an air electrode, a solid electrolyte, and a fuelelectrode, housed within a pressure vessel. Power is generated bysupplying compressed air to the air electrode and supplying fuel gas tothe fuel electrode. The fuel gas L2 supplied to the SOFC 13 is, forexample, liquefied natural gas (LNG).

A compressed air supply device (compressed air supply unit) 61 is linkedto the SOFC 13 via the second compressed air supply line 31, allowingcompressed air (second compressed air) A2 compressed by the compressedair supply device 61 to be supplied to an inlet of the air electrode. Acontrol valve (first on/off valve) 32 that can adjust the flow rate ofthe air supplied, and a blower 33 that can increase the pressure of thecompressed air A2 are provided along an air flow direction on the secondcompressed air supply line 31. An exhaust air line 34 into which exhaustair A3 that was used at the air electrode is discharged is connected tothe SOFC 13. The exhaust air line 34 branches into an exhaust line 35that discharges to the outside exhaust air A3 that was used at the airelectrode, and a compressed air circulation line 36 that is connected tothe combustor 22. A control valve 37 that can adjust the flow rate ofthe air discharged is provided on the exhaust line 35, and a controlvalve 38 that can adjust the flow rate of the circulating air isprovided on the compressed air circulation line 36.

Also, a second fuel gas supply line 41 is provided on the SOFC 13 tosupply the fuel gas L2 to the inlet of the fuel electrode. A controlvalve 42 that can adjust the supplied fuel gas flow rate is provided onthe second fuel gas supply line 41. The SOFC 13 is connected to anexhaust fuel line 43 in which exhaust fuel gas L3 that was used at thefuel electrode is discharged. The exhaust fuel line 43 branches into anexhaust line 44 that discharges to the outside, and an exhaust fuel gassupply line 45 connected to the combustor 22. A control valve 46 thatcan adjust the flow rate of the fuel gas discharged is provided on theexhaust line 44, and a control valve 47 that can adjust the flow rate ofthe fuel gas supplied and a blower 48 that can increase the pressure ofthe fuel are provided on the exhaust fuel gas supply line 45 along theflow direction of the fuel gas L3.

Also, a fuel gas recirculation line 49 is provided on the SOFC 13connecting the exhaust fuel line 43 and the second fuel gas supply line41. A recirculation blower 50 that recirculates the exhaust fuel gas L3of the exhaust fuel line 43 to the second fuel gas supply line 41 isprovided on the fuel gas recirculation line 49.

A turbine 52 of the steam turbine 14 is rotated by steam generated by anexhaust heat recovery boiler 51 (HRSG). The exhaust heat recovery boiler51 is connected to an exhaust gas line 53 from the gas turbine 11(turbine 23), and generates steam S by heat exchange between air andhigh-temperature exhaust gas G. A steam supply line 54 and a watersupply line 55 are provided between the steam turbine 14 (turbine 52)and the exhaust heat recovery boiler 51. A condenser 56 and a watersupply pump 57 are provided on the water supply line 55. The generator15 is provided coaxially with the turbine 52, and can generate power bythe rotation of the turbine 52. The exhaust gas from which the heat hasbeen recovered in the exhaust heat recovery boiler 51 is discharged tothe atmosphere after removal of harmful substances.

The compressed air supply system of the power generation system 10according to the first embodiment described above will now be describedin detail. As illustrated in FIG. 1, the power generation system 10according to the first embodiment is provided with a compressed airsupply device (compressed air supply unit) 61 capable of generatingcompressed air, and a second compressed air supply line 31 for supplyingcompressed air compressed by the compressed air supply device 61 to theSOFC 13.

Specifically, the compressed air supply device 61, which is capable ofstand-alone operation, is provided separately from the compressor 21 ofthe gas turbine 11, with the compressor 21 supplying compressed air onlyto the combustor 22 (turbine 23) via the first compressed air supplyline 26 and the compressed air supply device 61 supplying compressed aironly to the SOFC 13 via the second compressed air supply line 31.Therefore, total quantity of the compressed air compressed by thecompressor 21 is delivered to the combustor 22 and the turbine 23, andtotal quantity of compressed air compressed by the compressed air supplydevice 61 is delivered to the SOFC 13. As a result, fluctuations in theoperating state of the gas turbine 11 are not transmitted to the SOFC13, allowing the SOFC 13 to operate stably. Specifically, the SOFC 13generates power as the result of the compressed air A2 being supplied tothe air electrode and the fuel gas L2 being supplied to the fuelelectrode. In this case, if the pressure in the air electrode and thepressure in the fuel electrode are not roughly equal, a flow ofcompressed air A2 or fuel gas L2 between the air electrode and the fuelelectrode will be generated, causing the temperature of the SOFC 13 tofluctuate. In the present embodiment, the compressed air Al compressedby the compressor 21 is not supplied to the SOFC 13; rather, onlycompressed air A2 compressed by the compressed air supply device 61 issupplied to the SOFC 13, eliminating fluctuations in the pressure in theair electrode of the SOFC 13, and allowing the SOFC 13 to operatestably.

The compressed air supply device 61 is constituted by an SOFC compressor(fuel cell compressor) 62 and an SOFC steam turbine (fuel cell steamturbine) 63 linked by a coupling shaft 64 so as to be capable ofintegral rotation. One end of the second compressed air supply line 31is connected to the SOFC compressor 62 and the other end is connected tothe SOFC 13, and the SOFC compressor 62 compresses air taken in via anair intake line 65. The SOFC compressor 62 is driven by the rotation ofthe SOFC steam turbine 63 by steam generated by the heat recovery steamgenerator 51, and is capable of compressing air. Specifically, one endof a steam supply line 66 is connected to the steam supply line 54 forsupplying steam from the heat recovery steam generator 51 to the steamturbine 14 (turbine 52), and the other end is connected to the SOFCsteam turbine 63. The steam supply line 66 is provided with a controlvalve 67 that is capable of adjusting the amount of supplied steam.

A control device 68 is at least capable of adjusting the degree ofopening of the control valve 32 and the control valve 67 and controllingthe driving and stopping of the blower 33. Thus, when the SOFC 13 isoperating normally, the control device 68 opens the control valves 32,67 and supplies steam generated by the heat recovery steam generator 51to the SOFC steam turbine 63 via the steam supply line 54 to drive theSOFC compressor 62.

A bypass line 71 is provided that connects the first compressed airsupply line 26 and the second compressed air supply line 31, and thebypass line 71 is provided with a control valve (second on/off valve) 72that is capable of adjusting the flow rate of compressed air. Thecontrol device 68 is capable of adjusting the degree of opening of thecontrol valve 72. Specifically, when the SOFC 13 is operating normally,the control device 68 closes the control valve 72 so that compressed airA2 generated by the compressed air supply device 61 is not supplied tothe gas turbine 11, but is only supplied to the SOFC 13. Conversely,when the SOFC 13 is stopped, the control valve 72 is opened and thecontrol valve 32 is closed so that compressed air generated by thecompressed air supply device 61 is not supplied to the SOFC 13, but isonly supplied to the gas turbine 11.

The following is a description of the operation of the power generationsystem 10 according to the first embodiment. As illustrated in FIGS. 1and 2, when the power generation system 10 is activated, the gas turbine11, steam turbine 14, and SOFC 13 are activated in that order. Thecontrol device 68 is capable of controlling not only the control valve32 and the control valve 67, but also the other control valves.

First, in the gas turbine 11, the compressor 21 compresses the air A,and the combustor 22 mixes and burns the compressed air A1 and the fuelgas L1, the turbine 23 is rotated by the exhaust gas G, and thegenerator 12 starts to generate power. Next, in the steam turbine 14,the turbine 52 is rotated by the steam S generated by the exhaust heatrecovery boiler 51, and, as a result, the generator 15 starts togenerate power.

Next, in the SOFC 13, the control valve 67 is opened so that steamgenerated by the heat recovery steam generator 51 is supplied via thesteam supply line 66 to the SOFC steam turbine 63 of the compressed airsupply device 61. The SOFC steam turbine 63 then begins to rotate due tothe supplied steam, and the SOFC compressor 62 is rotatably driven insync, compressing the air A taken in via the air intake line 65. TheSOFC compressor 62 then supplies compressed air A2 to the SOFC 13 viathe second compressed air supply line 31, and the pressure begins toincrease.

At this time, with the control valve 37 of the exhaust line 35 and thecontrol valve 38 of the compressed air circulation line 36 closed andthe blower 33 of the second compressed air supply line 31 stopped, thecontrol valve 32 is opened. Compressed air A2 compressed by thecompressed air supply device 61 is then supplied to the SOFC 13 side viathe second compressed air supply line 31. In this way, the pressure onthe SOFC 13 side increases due to the supply of the compressed air A2.

On the other hand, in the SOFC 13, the fuel gas L2 is supplied to thefuel electrode side and the pressure starts to rise. With the controlvalve 46 of the exhaust line 44 and the control valve 47 of the exhaustfuel gas supply line 45 closed, and the blower 48 stopped, the controlvalve 42 of the second fuel gas supply line 41 is opened, and therecirculation blower 50 of the fuel gas recirculation line 49 is driven.Then, the fuel gas L2 is supplied to the SOFC 13 side from the secondfuel gas supply line 41, and the exhaust fuel gas L3 is recirculated bythe fuel gas recirculation line 49. In this way, the pressure on theSOFC 13 side increases due to the supply of the fuel gas L2.

When the pressure on the air electrode side of the SOFC 13 reaches apredetermined pressure, the control valve 32 is fully opened, and theblower 33 is driven. At the same time, the control valve 37 is openedand the exhaust air A3 from the SOFC 13 is discharged from the exhaustline 35. Then, the compressed air A2 is supplied to the SOFC 13 side bythe blower 33. At the same time, the control valve 46 is opened and theexhaust fuel gas L3 from the SOFC 13 is discharged from the exhaust line44. Then, when the pressure of the air electrode side and the pressureof the fuel electrode side of the SOFC 13 reach the target pressure,pressurization of the SOFC 13 is completed.

In the present embodiment, a compressed air supply device 61 and ablower 33 are provided, but the blower 33 may be omitted by controllingthe compressed air supply device 61. Specifically, the degree of openingof the control valve 67 may be adjusted so as to adjust the amount ofsteam supplied to the SOFC steam turbine 63, and the amount ofcompressed air A2 generated by the SOFC compressor 62 may be adjusted soas to adjust the amount of compressed air A2 supplied to the SOFC 13 andincrease the pressure in the SOFC 13. In this case, the omission of theblower 33 eliminates the need to open and close the control valve 32 andactivate the blower 33, allowing for reduced costs.

Then, when the reaction (power generation) of the SOFC 13 is stable andthe components of the exhaust air A3 and the exhaust fuel gas L3 arestable, the control valve 37 is closed, and the control valve 38 isopened. Then, the exhaust air A3 from the SOFC 13 is supplied to thecombustor 22 from the compressed air circulation line 36. Also, thecontrol valve 46 is closed, the control valve 47 is opened, and theblower 48 is driven. Then, the exhaust fuel gas L3 from the SOFC 13 issupplied to the combustor 22 from the exhaust fuel gas supply line 45.At this time, the flow rate of the fuel gas L1 supplied to the combustor22 from the first fuel gas supply line 27 is reduced.

At this time, total quantity of the compressed air A1 compressed by thecompressor 21 is supplied to the combustor 22 and the turbine 23 of thegas turbine 11, and total quantity of the compressed air A2 compressedby the compressed air supply device 61 is supplied to the SOFC 13. Thus,even if a fluctuation in the output of the gas turbine 11 occurs and thepressure of the air A1 compressed by the compressor 21 fluctuates, thereis no fluctuation in the pressure of the air A2 supplied to the SOFC 13.As a result, there is no fluctuation in the pressure in the airelectrode of the SOFC 13, the pressure in the air electrode and thepressure in the fuel electrode are roughly equal, and the SOFC 13 isstably operated regardless of the operating state of the gas turbine 11.

When the SOFC 13 stops operating, the control device 68 opens thecontrol valve 72 and closes the control valve 32 when the SOFC 13 isstopped, so that the compressed air A2 generated by the compressed airsupply device 61 is supplied not to the SOFC 13, but to the gas turbine11. When the SOFC 13 is operating normally, the compressed air A2generated by the compressed air supply device 61 is supplied to the SOFC13 and the used exhaust air A3 is supplied to the combustor 22 of thegas turbine 11 via the compressed air circulation line 36. Thus, whenthe operation of the SOFC 13 is stopped, the compressed air A2 generatedby the compressed air supply device 61 is not supplied to the SOFC 13,but is supplied directly to the combustor 22 of the gas turbine 11 viathe bypass line 71. As a result, roughly equal amounts of compressed airA2 are supplied to the gas turbine 11 both when the SOFC 13 is operatingnormally and when it is stopped, allowing for stable power generation byenabling full-load operation. Because exhaust fuel gas from the SOFC 13is not supplied to the combustor 22 of the gas turbine 11 when theoperation of the SOFC 13 is stopped, the amount of fuel gas supplied viathe first fuel gas supply line 27 must be increased.

As described above, the power generation system according to the firstembodiment comprises the gas turbine 11 having the compressor 21, thecombustor 22, and the turbine 23, the first compressed air supply line26 for supplying compressed air compressed by the compressor 21 to thecombustor 22, the SOFC 13 having the air electrode and the fuelelectrode, the compressed air supply device 61 capable of generatingcompressed air, and the second compressed air supply line 31 forsupplying compressed air compressed by the compressed air supply device61 to the SOFC 13.

Accordingly, the compressed air supply device 61 is provided separatelyfrom the compressor 21 of the gas turbine 11, air A1 compressed by thecompressor 21 is supplied to the combustor 22 via the first compressedair supply line 26, and air A2 compressed by the compressed air supplydevice 61 is supplied to the SOFC 13 via the second compressed airsupply line 31. Therefore, there is no fluctuation in the pressure ofthe air supplied to the SOFC 13 even if the pressure of the air suppliedto the combustor 22 fluctuates according to the operating state of thegas turbine 11. As a result, there is no fluctuation in the pressure inthe air electrode of the SOFC 13, the pressure in the air electrode andthe pressure in the fuel electrode are roughly equal, and the SOFC 13can be stably operated regardless of the operating state of the gasturbine 11.

The power generation system according to the first embodiment isprovided with the heat recovery steam generator 51 for generating steamusing exhaust gas from the gas turbine 11 and the steam turbine 14driven by the steam generated by the heat recovery steam generator 51,and the compressed air supply device 61 is provided with an SOFCcompressor 62 and a steam supply line 66 for supplying steam generatedby the heat recovery steam generator 51 to the SOFC steam turbine 63.Accordingly, when steam generated by the heat recovery steam generator51 is supplied to the SOFC steam turbine 63 via the steam supply line66, the SOFC steam turbine 63 is driven by the steam so that the SOFCcompressor 62 is driven to generate compressed air A2, which is suppliedto the SOFC 13. The power generation system 10 combines the SOFC 13, thegas turbine 11, and the steam turbine 14, and steam generated within thepower generation system 10 is used to drive the SOFC compressor 62 togenerate compressed air A2 which is supplied to the SOFC 13, therebyallowing overall system efficiency to be increased.

The power generation system of the first embodiment is provided with thecontrol valve 32 capable of opening and closing the second compressedair supply line 31, the bypass line 71 connecting the first compressedair supply line and the second compressed air supply line 31, and thecontrol valve 72 for opening and closing the bypass line 71.Accordingly, the compressed air A2 generated by driving the SOFCcompressor 62 can be supplied to the combustor 22 via the bypass line71, allowing the amount of compressed air to be adjusted according tothe operating state of the gas turbine 11 or the SOFC 13.

The power generation system of the first embodiment is provided with thecontrol device 68 capable of opening and closing the control valve 32and the control valve 72, and, when the SOFC 13 is stopped, the controldevice 68 closes the control valve 32 and opens the control valve 72.Accordingly, when the SOFC 13 is stopped, the control valve 32 is closedto stop the supply of compressed air A2 from the compressed air supplydevice 61 to the SOFC 13, and the control valve 72 is opened to beginsupplying compressed air A2 from the compressed air supply device 61 tothe combustor 22 of the gas turbine 11, ensuring the amount ofcompressed air provided to the gas turbine 11 and allowing the gasturbine 11 to operate stably.

Second Embodiment

FIG. 3 is a schematic view illustrating a compressed air supply line ina power generation system according to a second embodiment of thepresent invention. The basis configuration of the power generationsystem according to the present embodiment is roughly identical to thatof the first embodiment described above; thus, for parts described usingFIG. 2 and having similar functions as in the first embodiment describedabove, the same reference numerals are used, and detailed descriptionthereof will be omitted.

In the power generation system of the second embodiment, as illustratedin FIGS. 2 and 3, a compressed air supply device (compressed air supplyunit) 81 is linked to the SOFC 13 via the second compressed air supplyline 31, the compressed air supply device 81 being capable of supplyingcompressed air A2 to an inlet of the air electrode. Specifically, thecompressed air supply device 81, which is capable of stand-aloneoperation, is provided separately from the compressor 21 of the gasturbine 11, with the compressor 21 supplying compressed air A1 only tothe combustor 22 (turbine 23) via the first compressed air supply line26 and the compressed air supply device 81 supplying compressed air A2only to the SOFC 13 via the second compressed air supply line 31.Therefore, the total quantity of compressed air compressed by thecompressor 21 is delivered to the combustor 22 and the turbine 23, andthe total quantity of compressed air compressed by the compressed airsupply device 81 is delivered to the SOFC 13. As a result, fluctuationsin the operating state of the gas turbine 11 are not transmitted to theSOFC 13, allowing the SOFC 13 to operate stably.

The compressed air supply device 81 is constituted by an SOFC compressor(fuel cell compressor) 82 and a drive motor 83 linked by a couplingshaft 84. One end of the second compressed air supply line 31 isconnected to the SOFC compressor 82 and the other end is connected tothe SOFC 13, and the SOFC compressor 82 compresses air taken in via anair intake line 85. The SOFC compressor 82 is driven by power beingsupplied to the drive motor 83, and is capable of compressing air.

The control device 68 is at least capable of adjusting the degrees ofopening of the control valve 32 and the control valve 72 and controllingthe driving and stopping of the drive motor 83. Thus, when the SOFC 13is operating normally, the control device 68 opens the control valves32, 67, and the drive motor 83 is driven to drive the SOFC compressor82.

A bypass line 71 is provided that connects the first compressed airsupply line 26 and the second compressed air supply line 31, and thebypass line 71 is provided with a control valve 72 that is capable ofadjusting the flow rate of compressed air. When the SOFC 13 is operatingnormally, the control device 68 closes the control valve 72 so thatcompressed air generated by the compressed air supply device 81 is notsupplied to the gas turbine 11, but is only supplied to the SOFC 13.Conversely, when the SOFC 13 is stopped, the control valve 72 is openedand the control valve 32 is closed so that compressed air generated bythe compressed air supply device 81 is not supplied to the SOFC 13, butis only supplied to the gas turbine 11.

When the power generation system described above is activated, the gasturbine 11, steam turbine 14, and SOFC 13 are activated in that order;however, the SOFC 13 may also be activated before the gas turbine 11.

When operating the SOFC 13, the drive motor 83 is driven so as torotatably drive the SOFC compressor 82, compressing air A taken in viathe air intake line 85. The SOFC compressor 82 then supplies compressedair A2 to the SOFC 13 via the second compressed air supply line 31.Meanwhile, the control valve 42 of the second fuel gas supply line 41 isopened, thereby supplying fuel gas L2 to the SOFC 13 via the second fuelgas supply line 41. The compressed air A2 and the fuel gas L2 then reactin the SOFC 13, generating power.

At this time, total quantity of the air A1 compressed by the compressor21 is supplied to the combustor 22 and turbine 23 of the gas turbine 11,and total quantity of the air A2 compressed by the compressed air supplydevice 81 is supplied to the SOFC 13. Thus, even if a fluctuation in theoutput of the gas turbine 11 occurs and the pressure of the air A1compressed by the compressor 21 fluctuates, there is no fluctuation inthe pressure of the air A2 supplied to the SOFC 13, and the SOFC 13 isoperated stably regardless of the operating state of the gas turbine 11.

As described above, the power generation system according to the secondembodiment is provided with the gas turbine 11 having the compressor 21,the combustor 22, and the turbine 23, the first compressed air supplyline 26 for supplying compressed air compressed by the compressor 21 tothe combustor 22, the SOFC 13 having the air electrode and the fuelelectrode, the compressed air supply device 81 capable of generatingcompressed air, and the second compressed air supply line 31 forsupplying compressed air compressed by the compressed air supply device81 to the SOFC 13.

Accordingly, the compressed air supply device 81 is provided separatelyfrom the compressor 21 of the gas turbine 11, air A1 compressed by thecompressor 21 is supplied to the combustor 22 via the first compressedair supply line 26, and air A2 compressed by the compressed air supplydevice 81 is supplied to the SOFC 13 via the second compressed airsupply line 31. Therefore, there is no fluctuation in the pressure ofthe air supplied to the SOFC 13 even if the pressure of the air suppliedto the combustor 22 fluctuates according to the operating state of thegas turbine 11. As a result, the SOFC 13 can be stably operatedregardless of the operating state of the gas turbine 11.

In the power generation system according to the second embodiment, thecompressed air supply device 81 is provided with the SOFC compressor 82and the drive motor 83 for driving the SOFC compressor 82. Accordingly,the SOFC compressor 82 is driven by the drive motor 83 to generatecompressed air A2, which is supplied to the SOFC 13. Simply by providingthe drive motor 83 and the SOFC compressor 82, compressed air A2 can besupplied to the SOFC 13 independently of the gas turbine 11, allowingstable operation of the SOFC 13 to be ensured using a simpleconfiguration.

In the embodiments described above, the first on-off valve and thesecond on-off valve of the present invention are control valves 32, 72capable of adjusting flow rate, but these valves may be also be cutoffvalves incapable of adjusting flow rate.

REFERENCE SIGNS LIST

-   10 Power generation system-   11 Gas turbine-   12 Generator-   13 Solid oxide fuel cell (SOFC)-   14 Steam turbine-   15 Generator-   21 Compressor-   22 Combustor-   23 Turbine-   26 First compressed air supply line-   27 First fuel gas supply line-   31 Second compressed air supply line-   32 Control valve (first on-off valve)-   33 Blower-   34 Exhaust air line-   36 Compressed air circulation line-   41 Second fuel gas supply line-   42 Control valve-   43 Exhaust fuel line-   45 Exhaust fuel gas supply line-   49 Fuel gas recirculation line-   61 Compressed air supply device (compressed air supply unit)-   62 SOFC compressor (fuel cell compressor)-   63 SOFC steam turbine (fuel cell steam turbine)-   66 Steam supply line-   67 Control valve-   71 Bypass line-   72 Control valve (second on-off valve)

1. A power generation system comprising: a gas turbine having acompressor and a combustor; a first compressed air supply line forsupplying first compressed air compressed by the compressor to thecombustor; a fuel cell having an air electrode and a fuel electrode; acompressed air supply unit capable of generating second compressed air;a second compressed air supply line for supplying second compressed aircompressed by the compressed air supply unit to the fuel cell; a firston/off valve capable of opening and closing the second compressed airsupply line; a bypass line connecting the first compressed air supplyline and the second compressed air supply line; and a second on/offvalve for opening and closing the bypass line.